Method and apparatus for bleaching paper-pulp.



I. E. HEISKANEN.

METHO'D AN`D APPARATUS F0B BLEACHINGIPAPER PULP. APPpgcATlon FILED ria. 1. Isla.

1,2'?"`1,926.vv Pateted sept. 3,1918.

v 4 SHEETS-SHEET l.

gmwntoz attofmuf! APPLICATION FILED FEB-7.1918.

Patented Sept. 3, 1918.

4 SHEETS-SHEET 2.

vmwntoz aucun I. E. HEISKANEN.'

METHODAND APPARATUS FOR BLEACHING PAPER PULP.

APPLICATION mio ma. z. Isla.

1 ,277,926. Pat-entedSept. 3,1918.

4 SHEETS-SHEET 3.

annu/woz wil/naso I 'J. E. HEISKANEN.

METHOD AND APPARATUS FOR BLEACHING PAPER PULP.

APPLICATION FILED FEB. 7. 19H3. 1 ,277,926. Patented Sept. 3, 1918` 4 SHEETSSHET 4 jim... Q4

u w w GMM/buco@ akamu@ JALMAR E. HEISKANEN, OF CANTON, NORTH CAROLINA.

METHOD AND APPARATUS FOR BLEACHING PAPER-PULP.

Specification of Letters Patent.

Patented Sept. 3, 1918.

Application led February 7, 1918. Serial N o. 215,806.

T 0 all whom z'tmay concern:

Be it known that I, JAL-An E. HEISKA- NEN, a citizen of Finland, and a resident of Canton, county of Haywood, State of North Carolina. United States of America. have invented certain new and useful Improvements in Methods and )qiparatus for Bleaching Paper-Pulp, of which the follow ing is a full and clear specification.

In manufacturing pulp for paper-making purposes, the pulp is bleached in liquid form, the liquid containing only a small percentage of fiber, the greater part being water. At the present. time, the pulp is bleached by two main syst-ems. One of these systems is continuous in that the bleached pulp flows continuously out from one end of the system, while the unblcaohed pulp is fed in continuously at the other end. In this method, only thin liquid pulp can be bleached, as there has been no practical means yet devised, so far as I am aware, to convey thick pulp through the system. The system usually depends on gravity How, though sometimes pumps are used. The thickest pulp which can be bleached in these systems ranges from 25% to 3% dry pulp. The disadvantages of this prior continuous system are, (l), the great. amount of Water carried by the pulp requires an immense amount of steam for heating it during the bleaching process; (2), the bleaching agent is dissolved in such a great quantity of water that an excessive amount of bleach is necessary to insure proper bleaching; (3), as the bleach is scattered in a great quantity of liquid, the fibers of the pulp have not an even chance to come into contact with the bleaching agent, resulting in some fibers becoming over-bleached while others are not bleached enough. The over-bleached fibers may be entirely destroyed and lost during washing, through the line holes of the Washing machines. The result is an unevenlyfinished product and great loss of pulp.

There are also systems for thick pulp in which say 5% to 10% per cent pulp can be bleached, but these are intermittent and require great investment in equipment as well as more labor to operate. In these intermittent systems, once the pulp is fed into the system, it is circulated a predetermined time and then dumped into storage. The saving of steam for bleaching fiber in these intermittent systems is considerable over the system using thin pulp.

For my system hereinafter described in detail, I claim the good points of both systems just described. My system is continuous and very thick pulp containing 5% dry fiber can be employed. A bleached pulp very uniform in color and strength is obtained, and only one-half to one-third of thc steam is consumed as compared with s ,vstems employing thin pulp. Furtherniore, the saving of bleach in my system 1s considerable and loss of fiber is small. Again, less water has to be pumped, and, consequently, a reduction in power is made. hly system occupies only one-half the floor space required for the other systems and, consequently, the first cost of installation of equipment and buildings is comparatively low. A further advantage in my system is that the present continuous bleaching systems employing thin pulp can be readily converted to operate in accordance with my method.

In the drawings- Figure 1 is a plan view showing a preferred form of apparatus for carrying out my invention;

Fig. 2 is a vertical section on the line 2 2 of Fig. 1;

Fig. 3 is a horizontal sectional view on the line 3-3 of Fig. 2;

Fig. 4 is a vertical sectional view on the line 4.-1 of Fig. 1; and

Figs. 5 and 6 are detail views of one form of weir that I may employ.

In its preferred embodiment, my system consists of a plurality of tank units connected together in such manner that the pulp, during the bleaching operation, passes from the first unit successively through all the units and is finally discharged into an apparatus for extracting the bleach, the number of units as well as the size and proportions thereof being determined by the amount of pulp which has to be bleached in any particular time. Each unit consists of a vertical receiving tank o and a closely-adjacent vertical discharge tank b, these tanks having their bottom portions taperedv respectively to a cylindrical connecting passage c, considerably smaller in diameter than either of the tanks. In the present instance, this passage c is arranged vertically, and in this passage is mounted a screw-propeller d which is adapted to be rapidly rotated by means of a motor e arranged on the roof f of the tank structure. The operation of this screw-propeller forces the liquid carrying the bleach and the fiber from the tank a into the tank b, the action of the propeller not only causing movement of the pulp-carrying liquid from one tank to the other, but servin to separate the fibers which have a ten ency to gather together, so that the fibers will be insured a thorough and uniform contact with the bleach.

From the tank b, the pulp flows partly back into the tank a of the same unit and partly over into tank a of the next adjacent unit, weirs g and g being employed on the tops of the side walls of the tank b to regulate the flow of pulp. The capacity of the weir g is much greater than the capacity of vthe Weir g, so that much the larger part of the discharge from the tank b will go back into the tank a of the Same unit. The proportion of the liquid that passes over the Weir g4 into the next unit will be approximately the same in quantity as the amount of pulp fed into the apparatus at the first unit, so that a small percentage of the pulp will. be continuously fiowing from the inlet to the outlet of the machine, while the remaining pulp will be continuously circulating in the tank units. By my method of forcibly setting up an independent circulation of pulp in each of the tank units, I not only provide for giving all the fibers floated in the liquid an equal chance of being uniformly bleached, but I provide also for retaining the pulp in the apparatus a sufficient length of time to insure thorou h bleaching without employing a great num er of tanks, such as would be required if the pulp were merely passed along from tank to tank. A feature of importance lies also in the use of a propeller-pump submerged in the liquid and arranged in a passage between the two tank units in such manner as to avoid the formation of pockets, bafiles or other obstructions in the circulating space of each unit, whereby I insure a practically uniform movement of all the fibers and thus reduce waste to a minimum and obtain a superior product. To get the best results in this direction, I employ a throat or passage smaller in diameter than the diameter of the tanks and taper the bottom portions of the tanks toward said throat, but it will be understood that the tanks may be shaped in various ways and the propeller-screw may be arranged in any suitable position, so long as it is completely submerged in the liquid.

It will be observed particularly that I avoid the use of horizontal channels in my mixing and circulating elements, thereby preventing the pulp settling and caking up in any place in my system. It will be understood also that I may use any type of weir or valve for proportioning the fiow of liquid from the tank b into the adjacent tanks a.

Larme@ The thin liquid pulp from the pulp-mill is pumped by pipe A to concentrators B, Where the desired consistency of pulp is reached. The thickened pulp drops to the screw-conveyer C, which conveys the pulp to opening D, and thence falls to tank a of the bleaching unit. The pulp is circulated, as set forth, by the propeller-screws d. From the tank b of the last circulating unit, the pulp continuously overflows to the washing system, where the remaining bleach is separated. The fiow of the pulp over this last Weir-is always proportionate to the amount of pulp fed into the first unit, the length of bleaching time bein regulated by the amount of pulp fed 1n and by adjusting the weirs or gates g, g. From the last tank, the pulp flows to the bleach-extractor G. The water containing the bleach is either run into a sewer or used for diluting the pulp in the first tank if it be found that the concentration is too high. By pipe Y, wash water is added which is mixed with the pulp by agitator` W. The wash water is separated by washers H and H2, and the final uniformly-bleached pulp drops into storage tank I underneath. The bleaching agent is added by pipe N at the conveyer C, which thoroughly mixes the pulp and bleach, additional bleach being added by pipes R and R2, etc., as the case may require. Steam is supplied through the first tank particularly by pipe S, additional steam being added by pipes T and T2, etc., at the bottom of the tanks, these latter steam pipes being soarranged that the inflow of steam into the tank b assists in the circulation of the pulp, the discharge of steam into the laterally-projecting tapered part of this tank b being in the direction of flow of the pulp.

I provide pipes U for emptying the tanks or to wash a unit or to enable the unit to be by-passed for the purpose of making repairs, etc. A pump V connected to pipes U can be used for elevating the pul to the other units as the operator may esire. From pipes U a connection may be made to a sewer.

It will be obvious that many changes in the specific construction of my device may be made without departing from the spirit of my invention, and it will be particularly obvious to those skilled in the art that existing bleaching plants may be readily converted into my unit system of circulating the bleaching pulp.

The nature and scope of the invention having been thus indicated and its preferred embodiment having been specifically de' scribed, what is claimed as new is:

1. In a pulp bleaching apparatus, a plurality of circulating units each embodying a pair of tanks and means for propelling the pulp from one tank to the other, adjustable means being provided for permitting the pulp to flow partly back into the tank from which it was propelled and partly into the receiving tank of the next unit.

2. In an apparatus for bleaching pulp, a plurality of circulating units each embodying a pair of vertical tanks Whose bottom portions taper to a connecting passage, a screw-propeller in this passage and means for rot-ating this propeller, adjustable means being provided for regulating the ioW of pulp from unit to unit.

3. The method herein described for bleaching pulp consisting in causing it to continuously flow through a series of bleaching tank units, each of which embodies a plurality of; tanks, an independent circulation being maintained from tank to tank in leach unit While a portion of the pulp from each unit is continuously carried over to the next unit, the amount of pulp being con; tinuously carried over from unit to unit bein equal to the amount of pulp continuous y fed to the apparatus.

4. In a pulp bleaching apparatus, a plurality of circulating umts each embodying a pair of tanks and means for propelling the pulp from one tank to the other, means being provided for permittin the pulp to flow partly back into the tan it Was propelled and partly into the receiving tank of the next unit.

5. In an apparatus for bleaching pulp, a plurality of circulating units each embodying a pair of vertical tanks Whose bottom 35 tanks adjacent said throat portion being 45 tapered toward the same, said throat portion being located below the normal level of liquid, a screw propeller mounted in said throat portion, and means for rotating this propeller, means being provided for regu- 50 lating the ilovv of pulp from unit to unit.

In testimony whereof I hereunto afx my signature.

J ALMAR E. HEISKANEN.

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